OBJECTIVES: The purpose of this study was to analyze clinical features of the patients who underwent implantable cardioverter-defibrillator (ICD) treatment. METHODS: Clinical features and interrogation of intracardiac electrograms of the patients who had undergone ICD implantation between 1996 and 2005 at Asan Medical Center were retrospectively analyzed. RESULTS: One hundred thirty five patients (109 male, 27 female, a mean age of 54 짹 13 y.o.) were included. Underlying cardiovascular diseases were post-myocardial infarction(MI) ventricular tachycardia(VT) in 40 (29.6%), Brugada syndrome in 35(26%), hypertrophic cardiomyopathy(CM) in 23(17%), dilated CM in 13(9.6%) patients. Appropriate shocks were delivered in 43(31.9%) patients, 13(9.6%) with post-MI VT, 11(8.1%) with Brugada syndrome, 6(4.4%) with hypertrophic CM and 4(2.9%) with dilated CM. Inappropriate shocks were delivered in 39(28.9%) patients, 13(9.6%) with post-MI VT, 8(5.9%) with Brugada syndrome, 7(5.2%) with hypertrophic CM and 3(2.2%) with dilated CM. Inappropriate shocks were caused most commonly by atrial fibrillation with rapid ventricular responses. Other cuases were T wave oversensing or electromagnetic interference. Anti-tachycardia pacing therapy was effective in 17 patients. Major complications of ICD therapy during follow-up included ICD infection(1), lead problems(3), electromagnetic interference (1) and generator malfunction(35 pts). CONCLUSIONS: The three major cardiovascular diseases in patients with ICD implantation were post-MI VT, Brugada syndrome and hypertrophic CM. Inappropriate shocks were delivered in a significant proportion of the patients, which emphasize the need for an aggressive rate control strategy in patients with atrial fibrillation. Most complications of ICD therapy were caused by device malfunction